This invention relates to electronic counter measures (ECM) systems and in particular to systems that utilize main lobe shifting techniques to jam track while scan (TWS) radar operation.
One present ECM technique is to use a swept repeater modulation (SRM) program. Such a system merely transmits a series of pulses at a given frequency. A certain number of the pulses will coincide with threat radar signals in such a way as to introduce an angle error in the return signal. SRM programs when used against TWS emmiters are forced to reduce effectiveness by sweeping over the scan rate uncertainty of the emitter type of interest. As an alternative, many systems rely on external receivers, such as the radar homing and warning systems (RHAW) to measure the appropriate scan rate of each radar encountered and thereby permit the SRM program to reduce the scan rate uncertainty range being swept. This procedure has been found to produce a marked improvement in jamming effectiveness. The cost and complexity of the required signal processing equipment for RHAWs is often prohibitive, however. Another approach which has often been considered as an alternative to the SRW program is the main lobe shifting technique. The inherent advantage of this approach is that there exist no frequency or scan rate uncertainty in that each main lobe received is operated upon independently. In theory this should provide the main lobe shifting technique with a performance far exceeding that achieved with present SRM programs. However, in practice this has not always been the case and as a result main lobe shifting is not a widely used technique in todays ECM equipment. One problem that can be encountered is that initial detection of the received signal can occur anywhere on the main lobe or even on a side lobe. The conventional approach is to use log video amplifiers in an attempt to overcome this problem by locating the peak of the beam in order to properly position the up modulation interval. This however, is a difficult task which can be influenced by fluctuations in received power. A second problem of the conventional approach is that it is not effective against lobe on receive only (LORO) radar operation or other constant illuminator emmiter sources since discrete lobes cannot be detected. Further, it may even cease to be effective against TWS sources when in the presence of a constant illuminator.
It is apparent from the foregoing discussion that there currently exists the need for an improved ECM technique and implementation means that is effective in jamming all types of threat radar operation and that overcomes the scan rate frequency and phase uncertainties common to currently used techniques. The present invention is directed toward satisfying that need.